1. Field of the Invention
The present invention relates to a lintel configuration within a wall frame for use in building construction.
2. Description of the Prior Art
Wall frames for building construction, particularly for domestic buildings, are commonly prefabricated in a factory and then transported to site for speedy erection. A prefabricated wall frame will usually consist of one or more window, door or other openings to receive a prefabricated window or door frame which is installed or finished on site. Each such opening is spanned along its upper edge by a lintel to carry the loading applied to the top plate of the wall frame by trusses or other building components above the lintel. FIG. 1 shows a typical lintel configuration within a prefabricated wall frame. The portion of the frame shown in that Figure has a vertical jamb stud 2, a vertical prop stud 4 immediately adjacent the jamb stud, a horizontal top plate 6, and an additional horizontal top plate 8 above that. The lintel 10 spanning the door or window opening extends across the underside of the top plate 6 and is supported at its lower edge by the prop stud 4. The lintel in this case is formed by a wooden beam but it may alternatively be formed by a metal beam such as a light steel beam of channel cross-section. It will be noted that the prop stud 4 needs to be cut to a shorter length than the jamb stud 2 in order to support the underside of the lintel 10 and this is inconvenient in a factory situation involving the assembly of multiple frames where it is desirable to standardise to the maximum extent possible the pre-cut components needed to assembly the various frames.
In this case the prop stud 4 provides the majority of the support for the lintel with some load being transferred to the jamb stud 2 by virtue of the connections (usually nails) between the two. However, the jamb stud 2 mainly serves to provide continuity between the prop stud 4 and the top plate and has minor load bearing capacity. Since the prop stud 4 resists higher loads than the jamb stud 2 or the common studs in the wall frame, apart from being a different length it may need to be of a higher grade which is an added complication in the manufacturing process as it is then necessary to access a different grade of timber and to ensure that it is installed in that particular location in the frame. The increase in grade of the prop stud 4 may not always be sufficient to withstand the magnitude of the applied load and the prop stud 4 may have to be doubled or tripled. Without significant fixing between the prop stud 4 and the jamb stud 2 it is not possible to take advantage of the unused strength of the jamb stud 2.
Moreover, as would be understood, the stiffness of a lintel in the direction of the applied load (a vertical loading) is determined to a significant extent by its depth and with the configuration illustrated in FIG. 1 its depth is inherently limited by the height of the opening it is spanning and by the overall height of the wall frame and as a result, for increased stiffness to resist deflection, a substantial increase is needed in the thickness or bulk of the beam or in the grade or type. While an increase in the depth of the lintel could be achieved by removal of the top plate in the zone of the lintel, this leads to reduced lateral stability of the frame and also leads to other difficulties in the overall construction of the frame and is not a particularly desirable approach to achieving required lintel strength.